In shaders, `vec3` should be avoided for `std140` layout, as they take the size of a `vec4` and won't support manual padding by adding an additional `float`.
This change is needed for 3D to work in WebGL2. With it, I get PBR to render
<img width="1407" alt="Screenshot 2021-04-02 at 02 57 14" src="https://user-images.githubusercontent.com/8672791/113368551-5a3c2780-935f-11eb-8c8d-e9ba65b5ee98.png">
Without it, nothing renders... @cart Could this be considered for 0.5 release?
Also, I learned shaders 2 days ago, so don't hesitate to correct any issue or misunderstanding I may have
bevy_webgl2 PR in progress for Bevy 0.5 is here if you want to test: https://github.com/rparrett/bevy_webgl2/pull/1
9098df3034
